How do I connect two networks for specific applications?

Question

I have one LAN connection and another USB internet modem how I can use both same time for specific applications with out any overlapping?

Answer 1

Bridging Networks

Bridging multiple interfaces is a more advanced configuration, but is very useful in multiple scenarios. One scenario is setting up a bridge with multiple network interfaces, then using a firewall to filter traffic between two network segments. Another scenario is using bridge on a system with one interface to allow virtual machines direct access to the outside network. The following example covers the latter scenario.

Before configuring a bridge you will need to install the bridge-utils package. To install the package, in a terminal enter:

sudo apt-get install bridge-utils

Next, configure the bridge by editing /etc/network/interfaces:

auto lo
iface lo inet loopback

auto br0
iface br0 inet static
        address 192.168.0.10
        network 192.168.0.0
        netmask 255.255.255.0
        broadcast 192.168.0.255
        gateway 192.168.0.1
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

Enter the appropriate values for your physical interface and network.

Now restart networking to enable the bridge interface:

• How to restart the networking service?

The new bridge interface should now be up and running. The brctl provides useful information about the state of the bridge, controls which interfaces are part of the bridge, etc. See man brctl for more information.

This is taken directly from the Ubuntu Documentation: Network Configuration